The present invention relates to a magnetoresistive effect type of head for detecting intensity of a magnetic field utilizing a resistive change according to the intensity of the magnetic field, a manufacturing method of the magnetoresistive effect type of head, and an information-reproducing system for reproducing information stored in a storage medium.
As computers have come into wide use, a lot of information is dealt routinely recently. Such information is stored in a storage medium with a large number of physical marks such as directions of magnetization or existence of pits, and is reproduced by an information-reproducing system for reading those marks to produce an electric reproduction signal.
As a storage medium for storing information in form of a direction of magnetization, for example, there is a magnetic disk. The magnetic disk is partitioned into a large number of circumference-like shaped tracks. Each track having a predetermined track width is further partitioned into bit lengths each having a predetermined length to form the minimum unit addressed as one-bit area. The magnetic disk is made of a magnetic material in its surface and is independently magnetized for each one-bit area to store a bit of information in the respective one-bit area in accordance with a direction of magnetization of the one-bit area. A hard disk drive, which is an information-reproducing system for reproducing information stored in the magnetic disk, has a magnetic head for detecting an external magnetic field for reproduction. This magnetic head for reproduction is disposed so as to be close to or in contact with the respective one-bit area of the magnetic disk and detects a magnetic field generated in accordance with a state of the magnetization of the one-bit areas, so that electric reproduction signals are created, and reproduces information stored in the magnetic disk.
Every year a storage density of information stored in a magnetic disk is enhanced, and as the storage density is enhanced, a size of the respective one-bit area of the magnetic disk is reduced. In order to detect a direction of the magnetization of the one-bit area small in size, there is needed a magnetic head for reproduction which is highly sensitive.
As the magnetic head for reproduction which is highly sensitive, there is known a magnetoresistive effect type of head (MR head) utilizing the magnetoresistive effect in which a resistance is varied in accordance with an external magnetic field. As a particularly highly sensitive one of the MR heads, there is known a spin valve type of MR head. The spin valve type of MR head is a multi-layer film including a magnetoresistive effect element comprising a free magnetic layer varying in a direction of magnetization in accordance with an external magnetic field, a non-magnetic metal layer, a fixed magnetic layer fixed in a direction of magnetization, and an antiferromagnetic layer for fixing a direction of magnetization of the fixed magnetic layer. In the spin valve type of MR head, a resistance is greatly varied in accordance with a relative angle between a direction of the fixed magnetic layer and a direction of the free magnetic layer. This magnetoresistive effect element is provided with an electrode layer through which a current conducts into the magnetoresistive effect element. In this spin valve type of MR head, a plane vertical to the multi-layer film serves as a receiving section to be sequentially close to or in contact with the respective one-bit area of the magnetic disk, so that the spin valve type of MR head receives a magnetic field generated from magnetization of the one-bit area to create an electric reproduction signal utilizing a variation of a resistance according to the received magnetic field.
The free magnetic layer of the multi-layer film is easy to involve a magnetic wall on edge portions or the like. When the magnetic wall moves owing to a variation of the magnetic field from the exterior, Barkhausen noise is generated on the reproduction signal. In order to suppress the generation of Barkhausen noise, a magnetic wall control layer made of a soft magnetic material and the like is disposed in form of a part of the multi-layer film. The magnetic wall control layer has a static magnetic field effect on the free magnetic layer and suppresses a movement of the magnetic wall of the free magnetic layer by the exchange coupling with the free magnetic layer.
With respect to such a spin valve type of MR head, one, in which the magnetoresistive effect element is formed in such a regular order that the free magnetic layer, the non-magnetic metal layer, the fixed magnetic layer, and the antiferromagnetic layer are laminated in the named order in turn from the bottom, is more satisfactory in orientation of magnetization of the laminated fixed magnetic layer and is more sensitive as compared with one, in which the magnetoresistive effect element is formed in the reverse order opposite to the regular order. For this reason, in many of the spin valve type of MR heads, the magnetoresistive effect element is formed in the regular order, and an electrode layer is laminated on the antiferromagnetic layer which is the top layer of the magnetoresistive effect element.
However, since the antiferromagnetic layer is large in specific resistance, laminating the electrode layer on the antiferromagnetic layer makes it difficult to conduct a current flowing from the electrode layer to the free magnetic layer, the non-magnetic metal layer and the fixed magnetic layer of the magnetoresistive effect element, which are directly involved in the detection of the magnetic field. Thus, there is considered a spin valve type of MR head in which in order to effectively conduct a current from the electrode layer to those layers, the electrode layer is disposed below the magnetoresistive effect element to improve sensitivity.
However, such a spin valve type of MR head, in which the electrode layer is disposed below the magnetoresistive effect element, is associated with a problem that the above-mentioned Barkhausen noise will be easily generated.
In view of the foregoing, it is an object of the present invention to provide a spin valve type of magnetoresistive effect type of head for preferably reproducing information recorded on a recording medium with high recording density suppressing generation of Barkhausen noise, a manufacturing method of the magnetoresistive effect type of head, and an information-reproducing system.
To achieve the above-mentioned object, the present invention provides a magnetoresistive effect type of head having a magnetoresistive effect element offering a resistive change according to intensity of an external magnetic field, for detecting a magnitude of a resistance of the magnetoresistive effect element to detect intensity of a magnetic field,
wherein said magnetoresistive effect element consists of a flat multi-layer film in which a free magnetic layer changing in a direction of a magnetization in accordance with the external magnetic field is set up to a lowest layer, and
said magnetoresistive effect type of head comprises:
a non-magnetic substrate;
an insulating layer contacting with-a center portion of a lower surface at a substrate side of said free magnetic layer;
a pair of electrode layers for conducting a current through said magnetoresistive effect element, said pair of electrode layers being formed at a position interposing said insulating layer therebetween contacting both edge portions of the lower surface at the substrate side of said free magnetic layer, and being formed with a same surface height as a surface height of said insulating layer; and
a pair of magnetic wall control layers for suppressing a movement of a magnetic wall of said free magnetic layer, said pair of magnetic wall control layers being formed to extend interposing said magnetoresistive effect element therebetween.
As will be described later in the preferred embodiments, according to the magnetoresistive effect type of head, first, a pair of electrode layers contacts both edge portions of the lower surface at the substrate side of said free magnetic layer. Thus, an interval between the pair of electrode layers causes a width (a core width) of a sensing area for sensing the magnetic field to be defined with great accuracy, and thereby preferably reproducing information stored in the magnetic disk with high storage density. Further, according to the magnetoresistive effect type of head, the pair of electrode layers is formed at a position contacting both edge portions of the lower surface of said free magnetic layer. This feature makes it possible to efficiently conduct a current through the magnetoresistive effect element and thereby detecting a magnetic field with high sensitivity. Furthermore, according to the magnetoresistive effect type of head, while the free magnetic layer is located on the pair of electrode layers, the pair of electrode layers is formed at the position interposing the insulating layer and is formed with the same surface height as a height of a surface of the insulating layer. Thus, the free magnetic layer has no difference in level and maintains flatness extending over the whole surface of the free magnetic layer. This flatness causes a movement of the magnetic wall of the free magnetic layer to be effectively suppressed by the magnetic wall control layer. Accordingly, the magnetoresistive effect type of head may suppress generation of Barkhausen noise and detect a magnetic field.
In the magnetoresistive effect type of head according to the present invention as mentioned above, it is preferable that the insulating layer contacting with the center portion of the lower surface of said free magnetic layer is an insulating layer which further extends below said pair of electrode layers, and
said insulating layer is formed in such a manner that thickness of a layer of a portion extending to the center portion of the lower surface of said free magnetic layer, of said insulating layer is thinner than thickness of a layer of a portion extending below said pair of electrode layers, of said insulating layer.
Generally, in order that information stored in the magnetic disk with high density is preferably reproduced, it is desired to achieve thinner layer of the insulating layer of the magnetic head.
According to the magnetoresistive effect type of head, the insulating layer is formed as mentioned above. Thus, the insulating layer portion, which contacts the center portion of the lower surface of said free magnetic layer, is provided in form of the thinner layer. The insulating layer portion has an effect on reproduction characteristics of information stored in the magnetic disk with high density. And thus, it is possible to effectively prevent leakage of a current from the electrode and the magnetoresistive effect element.
In the magnetoresistive effect type of head according to the present invention as mentioned above, it is preferable that said pair of electrode layers consists of a material including at least one of Gold Au and Copper Cu.
Since the Gold Au and Copper Cu are small in specific resistance, according to the magnetoresistive effect type of head, it is possible to achieve thinner layer of the electrode layer.
To achieve the above-mentioned object, the present invention provides a manufacturing method for a magnetoresistive effect type of head of manufacturing a magnetoresistive effect type of head having a magnetoresistive effect element offering a resistive change according to intensity of an external magnetic field, for detecting a magnitude of a resistance of the magnetoresistive effect element to detect intensity of a magnetic field, wherein said magnetoresistive effect element is a multi-layer film including a free magnetic layer changing in a direction of a magnetization in accordance with the external magnetic field is set up to a lowest layer, said manufacturing method for a magnetoresistive effect type of head comprises steps of:
forming a lower shield layer having a hill portion rising over a predetermined width in height;
forming on said lower shield layer an insulating layer thinner than height of said hill portion;
forming on said insulating layer an electrode layer consisting of a conductive material in which a surface height of a portion out of said hill portion is higher than a surface height of said hill portion;
providing a flatness in such a height that while said insulating layer appears on an upper surface of said hill portion, said electrode layer appears on a surface of a portion out of said hill portion;
forming the magnetoresistive effect element consisting of the multi-layer film in which the free magnetic layer changing in a direction of a magnetization in accordance with the external magnetic field is set up to the lowest layer in such a manner that the insulating layer appearing on the surface is in contact with the center portion of the lower surface of said free magnetic layer, and both the edge portions of the lower surface of said free magnetic layer contact a pair of electrode layers separated into a state interposing the insulating layer therebetween; and
forming a pair of magnetic wall control layers for suppressing a movement of a magnetic wall of said free magnetic layer, said pair of magnetic wall control layers being formed to extend interposing said magnetoresistive effect element therebetween.
According to the above-mentioned manufacturing method for a magnetoresistive effect type of head, similar to the magnetoresistive effect type of head as mentioned above, it is possible to manufacture a magnetoresistive effect type of head having a pair of electrode layers for conducting a current through said magnetoresistive effect element, said pair of electrode layers being formed at a position interposing said insulating layer therebetween contacting both edge portions of the lower surface at the substrate side of said free magnetic layer, and being formed with a same surface height as a surface height of said insulating layer.
To achieve the above-mentioned object, the present invention provides an information-reproducing system having a magnetic head disposed close to or in contact with a magnetic storage medium storing information by magnetization for detecting the magnetization of respective points of the magnetic storage medium, said information-reproducing system reproducing information according to the magnetization of respective points of the magnetic storage medium detected by said magnetic head,
wherein said magnetoresistive effect element consists of a flat multi-layer film in which a free magnetic layer changing in a direction of a magnetization in accordance with the external magnetic field is set up to a lowest layer, and
said magnetic head comprises:
a non-magnetic substrate;
an insulating layer contacting a center portion of a lower surface at a substrate side of said free magnetic layer;
a pair of electrode layers for conducting a current through said magnetoresistive effect element, said pair of electrode layers being formed at a position interposing said insulating layer therebetween contacting both edge portions of the lower surface at the substrate side of said free magnetic layer, and being formed with a same surface height as a surface height of said insulating layer; and
a pair of magnetic wall control layers extending interposing said magnetoresistive effect element therebetween.
According to the magnetic head of the information-reproducing system, similar to the above-mentioned magnetoresistive effect type of head, the pair of electrode layers is formed at a position contacting both edge portions of the lower surface of said free magnetic layer, and the free magnetic layer has no difference in level and maintains flatness extending over the whole surface of the free magnetic layer. Thus, according to the information-reproducing system, a magnetic field is detected with high sensitivity so that information stored in the magnetic disk with high recording density is preferably reproduced. And further, it is possible to suppress generation of Barkhausen noise when the magnetic field is detected.
As mentioned above, according to the present invention, it is possible to provide a magnetoresistive effect type of head for preferably reproducing information recorded on a recording medium with high recording density suppressing generation of Barkhausen noise, a manufacturing method of the magnetoresistive effect type of head, and an information-reproducing system.